The transport of sheets and sheet transfer in multi-color sheet printing machines by means of gripper cars and endless chains is known, as disclosed in German patent DE 3 636 578 A1. During the sheet transfer operation, as the gripper cars proceed around the wheels about which the chains are trained, the gripper cars experience a flexure as a result of centrifugal force dependent on the printing speed. Gripper car locking devices, such as shown in German patent DE-AS 1 224 753, obviate the centrifugal force effects on the gripper car by means of a plurality of hooks which connect the gripper car rigidly to the chain wheel shaft during the transfer period. Such locking devices, however, require a complex control mechanism in order to achieve the opening and closing movements.
In order to prevent the effect of flexure of the gripper cars during their deflection as they proceed about the chain wheels, it also is know from German patent DE-PS 2 157 993 to reduce the heights of the gripper supports over the width of the gripper car, continuously from the outside towards the middle, in accordance with the bending line. In such devices, care is taken to ensure that the differences in the heights of the gripper supports are designed to correspond to the bending line at maximum centrifugal force. Since the gripper supports lie on a straight line only at that centrifugal force, the sheet is subject to varying distortion in the transfer position at other speeds so that register problems still may occur and must be corrected.
Numerous publications disclose means for register correction or for the alignment of distorted sheets by means of adjustable bending devices. The bending devices, in accordance with German patent DE-PS 3 112 964, for example, relate generally to sheet transfer drums such as sheet feed and run-over drums. In the case of sheet transfer drums, a gripper carrier is pivotable relative to rotary movement of the drum, the position of a middle gripper carrier bearing being established by the instantaneous rotary position of an adjustable control cam mechanism comprising an outer cam on a control shaft and a biasing roller running against the outer cam with pre-stressing.
In German patent DE-Gbm 8 816 641, the bending devices also relate to an oscillating gripper, the bending devices consisting of an adjustable abutment which is fixed with respect to the side column of the press and against which a gripper carrier bears approximately centrally before the ends of the gripper carrier have reached their zero position, in which the grippers take over the sheet.
Finally, in German patent DE-OS 3 823 846, the bending devices relate to a sheet guide cylinder which comprises a non-rotating cross-member in the region of the cylinder mountings and which, in the central axial zone of the cylinder member, there is provided an adjustable support bearing that is mounted eccentrically in relation to the cross-member, the latter being rotatable and lockable on the frame so that the required flexure of the cylinder can be achieved by the adjustable middle support bearing.
The known bending devices thus relate to drum transfer systems and oscillating or auxiliary grippers, but not to chain transfer systems.